The damascene process is a process in which metal interconnect lines are delineated and isolated in dielectrics by means of chemical mechanical polishing (CMP). A dual damascene process is a similar process in which metal interconnect lines and vias (i.e., conductor-filled channels) are defined independently in photolithography and etch but metallized simultaneously.
Time Dependent Dielectric Breakdown (TDDB), in which a weakness in an insulator develops over time into a failure under a bias condition, is a significant source of reliability fails in the interconnection of devices in integrated circuits.
In the particular case of copper interconnect structures, the majority of TDDB fails occur in the upper portion of the copper line, often caused by a weak liner near the interface between the copper fill and the dielectric cap over the line.
Often times TDDB fails occur in the metal interconnections. For example, short circuits may be caused by residual metal (e.g., copper (Cu)) or liner materials (e.g., titanium (Ti), titanium nitride (TiN), tantalum (Ta), tantalum nitride (TaN), tungsten (W), etc.) that is not removed from the dielectric material by the CMP during the damascene or dual damascene process.
It is known that TDDB reliability can be improved by increasing the thickness of the liner material that confines the copper within the interconnect structure, but a uniform liner thickness increase on all covered surfaces reduces the amount of copper in the structure for a given interconnect dimension and is not acceptable.
One known failure mode is the presence of Cu (and/or Ta) particles between adjacent metal lines. It is known that such particles can be left by incomplete chemical-mechanical polishing (CMP) of the damascene interconnect. If the interconnect diffusion barrier liner were thicker in the transverse dimension (perpendicular to the interconnect member axis and parallel to the surface of the interlevel dielectric (ILD) that contains the interconnect) the metal particles would have to travel a larger distance before they could cause a short circuit between adjacent lines and reliability would be improved.
As noted above, the simple solution of thickening the liner uniformly on all covered surfaces is not acceptable because of the constant need to reduce the dimension of circuit elements.
The art could benefit from an interconnect structure that maintained an acceptable conductivity by supplying a sufficient cross section of copper material while also maintaining sufficient thickness of liner to reduce this failure mode.